This invention relates to test equipment and test techniques, especially equipment and techniques for testing electronic devices such as integrated circuits.
Integrated circuits (xe2x80x9cICsxe2x80x9d) can be tested in various ways. One test technique is to electrically stimulate an IC and then monitor its electrical response, typically by comparing the actual response to a reference response. The stimulation/response-monitoring technique is commonly performed with automated test equipment connected to the external electrical leads, commonly referred to as pins, by which the IC interacts with the outside world. The test equipment stimulates the IC by providing electrical signals to the IC""s pins and then monitoring the resultant electrical signals provided from the IC on its pins.
Another test technique involves probing an IC, especially when the IC has failed and it is desirable to determine the reason(s) for failure. The probing technique can be done by directing radiation, such as light or electrons, toward parts of the IC.
FIG. 1 illustrates a conventional test system that combines a stimulation/response-monitoring technique with an electron-beam probing capability for testing an integrated circuit 10 referred to generally as a device under test (xe2x80x9cDUTxe2x80x9d). The test system in FIG. 1 consists of core automated test equipment 12, manipulator 14, test head 16, tester load board 18, interface module 20, device-side load board (or card) 22, and electron-beam probe system 24 which contains an electron-beam probe (not separately shown). DUT 10 is situated in probe system 24 and attached to device-side board 22 also situated in probe system 24.
Interface module 20 interfaces between probe system 24 and test head 16. Module 20 consists of tester-side body 26, device-side body 28, and flexible electrical cables 30 which pass through openings in bodies 26 and 28 to connect tester board 18 to device-side board 22. Tester board 18, which electrically connects head 16 to electrical cables 30 along tester-side body 26, is customized to match head 16. Different implementations of board 18 permit interface module 20 to be utilized with different versions of head 16. Device-side board 22, which connects cables 30 to the pins of DUT 10, is similarly customized for testing DUT 10. Different versions of board 22 enable module 20 to be employed with different types of DUT 10.
During test operation, test equipment 12 generates electrical signals which are supplied through components 14, 16, 18, 20, and 22 to stimulate DUT 10. The resulting electrical response from DUT 10 is then furnished in the other direction through components 22, 20, 18, 16, and 14 to test equipment 12 for evaluation. The electron-beam probe in probe system 24 probes DUT 10 to form an image of a portion of DUT 10. The probing may be done as test signals generated by equipment 12 are used to stimulate DUT 10. The flexible nature of cables 30 in interface module 20 substantially prevents vibrations in test head 16 from being transmitted through module 20 to probe system 24.
Production units of an IC are commonly tested with automated test equipment in which a unit of the IC is attached to a production load board mounted directly on the test head of the automated test equipment. When the IC is also to undergo composite electrical testing/electron-beam probing using the test system of FIG. 1, device-side load board 22 is an additional load board that must be provided. That is, testing the IC entails designing two different types of custom load boards, device-side board 22 and the production load board mounted directly on the test head.
Rincon et al (xe2x80x9cRinconxe2x80x9d), xe2x80x9cA Custom Direct Dock High Speed Load Module and Lid for IDS Diagnostic Systemsxe2x80x9d, IDS User Conf. Advanced Training, Aug. 14, 1997, pages 1-5, describes how production testing of an IC and composite electrical testing/electron-beam probing of the IC can be done with only one custom load board. FIG. 2 illustrates a somewhat simplified version of part of the test system employed by Rincon for performing composite electrical testing/electron-beam probing. Heat-exchange equipment, alignment features, and attachment hardware (bolts and screws) are not shown in FIG. 2 to avoid illustration complexity.
For composite electrical testing/electron-beam probing, Rincon employs interface apparatus 32 for connecting electron-beam probe system 24, a lid-modified variation of the Schlumberger IDS 10000(copyright) electron-beam probe system, to test head 16 of a Texas Instruments V-Series tester. The components of interface apparatus 32 include (a) main body 34, (b) spring-loaded probes 36 that extend through openings in main body 34, (c) vacuum seal board 38 that contacts test head 16, and (d) vacuum seal ring 40 for hermetically sealing main body 34 to seal board 38 so as to maintain DUT 10 in a high vacuum provided by probe system 24. Main body 34 is formed with three plates (not separately shown) bolted to each other. Spring-loaded probes 36 electrically connect seal board 38 to customized production load board 42 that receives DUT 10 along an opening in board 42.
Lock ring 44 locks main body 34 of interface apparatus 32 to test head 16. Another lock ring (not shown) locks load board 42 to main body 34 situated on lid 46 of probe system 24. Item 48 in FIG. 2 is a vacuum seal ring for hermetically sealing main body 34 to lid 46. Item 50 is a column of the electron-beam probe. Opposite to what is illustrated in FIG. 2, DUT 10 can be mounted on the bottom side of load board 42. In that case, spacers are placed between lid 46 and main body 34 to adjust the position of DUT 10 above probe column 50.
By utilizing production load board 42 in the test system of FIG. 2, Rincon provides an economic advantage because only one type of custom load board needs to be designed to perform both production testing and composite electrical testing/electron-beam probing. However, vibrations can occur in test head 16. These vibrations can be readily transmitted through lock ring 44 and main body 34 to probe system 24. While the vibrations may not seriously impair the performance of the electron-beam probe, such vibrations can significantly impair the performance of certain other types of probes such as optical probes.
It is desirable to have a capability for performing electrical testing/probing with a composite test system in which the transmission of test-head vibrations to the probe is substantially avoided and in which units of the device under test are mounted on a load board that can be directly attached to the test head for additional, typically production, testing.
The present invention provides such a test capability. In accordance with the invention, a system for testing an electronic device contains one or more test heads, one or more load boards for receiving units of the electronic device, a probe system having a probe, and an interface apparatus. When there are two or more load boards, the load boards have largely identical patterns of test-head signal transmission positions.
The test system is deployable in a direct configuration and in an interface configuration. In the direct configuration, one such load board is attached directly to one such test head for transmitting test signals through that board""s signal transmission positions. One or more test operations are performed according to the invention as the load board receives a unit of the electronic device.
In the interface configuration, one such load board is coupled through the interface apparatus to one such test head for transmitting test signals through that board""s signal transmission positions. The probe system contacts the interface apparatus or/and the load board. One or more test operations are performed according to the invention as the load board receives a unit of the electronic device. Importantly, the interface apparatus is configured to largely prevent vibrations in the test head from being transferred through the interface apparatus to the probe system. As a result, the probe can be an optical or other probe highly sensitive to vibrations of the type that occur in the test head. The probe can, of course, also be an electron-beam or other probe of lesser sensitivity to such vibrations.
The isolation of the probe system from vibrations that occur in the test head is preferably achieved by configuring the interface apparatus to include a tester-side structure, a device-side body, and a vibration isolation system. The tester-side structure is attached to the test head. The device-side body is attached to the load board. The vibration isolation system, typically implemented with electrical cables, flexibly connects the tester-side structure to the device-side body while largely preventing vibrations in the tester-side structure from being transferred through the isolation system to the device-side body. Vibrations transferred from the test head to the tester-side structure are largely prevented from reaching the device-side body and thus are largely prevented from being transferred to the probe system.
In addition to, or as an alternative to, isolating the probe system from vibrations that occur in the test head, a substantial vacuum typically provided through the test head is employed to attach the load board to the interface apparatus and typically also to attach the interface apparatus to the test head. As used here, vacuum attachment of two bodies situated in an environment at some pressure external to the bodies means that the two bodies are attached to each other along a region at a pressure below the external pressure, typically 1 atmosphere, such that the external pressure exerted elsewhere on the bodies holds them in largely a fixed positional relationship to each other. The pressure in the vacuum-attachment region can be a substantial fraction of the external pressure and thus need not be at a high vacuum level such as that in free space.
In contrast to the electrical testing/electron-beam probing configuration of Rincon in which the interface apparatus and production load board are mechanically attached to the test head, the present vacuum attachment capability avoids the use of mechanical attachment equipment and thus is relatively simple. Also, vacuum attaching the load board and interface apparatus to the test head in the present invention takes advantage of the vacuum capability provided in certain test heads for vacuum attaching load boards directly to the test heads.
Regardless of whether one, or more than one, load board is employed in testing an electronic device according to both configurations of the present test system, the present invention only requires that one type of load board be designed because, in the case where two or more load boards are employed, the load boards have substantially the same pattern of test-head signal transmission positions. The invention thereby achieves the load-board economic advantage of Rincon""s test system while simultaneously going beyond Rincon by allowing a vibration-sensitive probe, such as an optical probe, to be employed in the interface configuration of the present test system. Accordingly, the invention provides a significant advance over the prior art.